This invention relates to an improved electrosurgical instrument and method for cauterization, coagulation and/or tissue welding in the performance of surgical procedures, especially endoscopic procedures.
Surgical procedures requiring cutting of tissue can cause bleeding at the site of the cutting. Before surgeons had the means to control bleeding many surgical procedures were quite difficult to perform because of excessive blood loss. Hemostasis is even more crucial in endoscopic or laparoscopic surgery where if the bleeding is not kept under control, the laparoscopy must be abandoned and the patient""s body cut to perform open surgery so that inaccessible bleeding may be controlled.
Thus, various techniques have been adapted to control bleeding with varying degrees of success such as, for example, suturing, applying clips to blood vessels, and stapling, as well as electrocautery and other thermogenic techniques. Advances in tissue joining, tissue repair and wound closure also have permitted surgical procedures previously not possible or too risky.
Initially, suturing was one of the primary means for providing hemostasis and joining tissue. Before other hemostatic and tissue repair means were introduced, surgeons had to spend a great deal of time sewing the tissue of patients back together.
Surgical clips were introduced as a means to close off blood vessels, particularly when cutting highly vascularized tissue. Application of surgical clips, however, can be cumbersome in certain procedures. The vessels must be identified. Then a clip must be individually applied on both sides of the intended cut of each identified vessel. Also, it may be difficult to find some vessels, particularly where the vessel is surrounded by fatty tissue.
Surgical staplers have been effective in decreasing the amount of time it takes to fasten tissue together. There are various types of surgical staplers. Staplers have been used for tissue joining, and to provide hemostasis in conjunction with tissue cutting. Such devices include, for example, linear and circular cutting and stapling instruments. Typically, a linear cutter has parallel rows of staples with a slot for a cutting means to travel between the rows of staples. This type of surgical stapler secures tissue for improved cutting, joins layers of tissue, and provides hemostasis by applying parallel rows of staples to layers of surrounding tissue as the cutting means cuts between the parallel rows. These types of cutting and stapling devices have been used successfully in procedures involving fleshy tissue such as muscle or bowel, particularly in bowel resection procedures. Circular cutting and stapling devices have successfully been used, for example, in anastomotic procedures where a lumen is rejoined. However, the results with cutting and stapling devices have been less than optimum where the procedure involves cutting highly vascularized tissue, such as mesentery or adnexa, which are prone to having hemostasis problems.
Electrocautery devices have also been used for effecting hemostasis. Monopolar devices utilize one electrode associated with a cutting or cauterizing instrument and a remote return electrode, usually adhered externally to the patient. More recently, bipolar instruments have been used because the cauterizing current is generally limited to tissue between two electrodes of the instrument.
Bipolar forceps have been used for cutting and/or coagulation in various procedures. For example, bipolar forceps have been used in sterilization procedures where the fallopian tubes are sealed off. Generally, bipolar forceps grasp tissue between two poles and apply electrical current through the grasped tissue. Bipolar forceps, however, have certain drawbacks, some of which include the tendency of the current to arc between poles when tissue is thin or the forceps to short when the poles of the forceps touch. The use of forceps for coagulation is also very technique dependent and the forceps are not adapted to simultaneously cauterize a larger area of tissue.
Bipolar scissors have been disclosed where two scissors blades act as two electrodes having insulated shearing surfaces. This device mechanically cuts tissue as coagulating electrical current is delivered to tissue in the current path. Bipolar scissors are also highly technique dependent in their use.
In prior devices, such as the device described in U.S. Pat. No. 5,403,312, electrosurgical energy has been delivered to biologic tissue in order to create a region of coagulation, as, for example, on either side of an incision, thus preventing blood and other bodily fluids from leaking out of the incision. In such a device, if tissue grasped by the jaws is compressed too much by applying excessive pressure to the region of coagulation, the tissue grasped by the end effector may be torn or crushed. If the tissue is not compressed enough because to little pressure is applied to the region of coagulation, the tissue in the region of coagulation may not be not effectively or uniformly cauterized because fluid (e.g. blood) could remain in the region of cauterization. In prior art devices, the surgeon has used tactile feedback and visual clues to determine the amount of pressure to apply to the region in order to obtain optimum coagulation. In instruments wherein the region of coagulation is partially or fully obscured, either by the end effector or by tissue, and is, therefore, not visible to the surgeon, it is particularly difficult for the surgeon to ensure that the appropriate pressure is being applied by the end effectors to ensure proper coagulation. It would, therefore, be advantageous to develop an electrosurgical instrument wherein the surgeon is not required to adjust the pressure applied by the end effector prior to applying electrosurgical energy to tissue in the region of coagulation. It would further be advantageous to design an instrument wherein the pressure applied to the tissue prior to coagulation is within a predetermined range.
One known method of varying the pressure applied to the tissue by the jaws of the end effector involves varying the gap between the jaws depending upon the tissue being grasped. However, such an arrangement would necessitate the use of different instruments, different end effectors or different staple cartridges depending upon the tissue being grasped. It would, therefore, be advantageous to design an instrument wherein the pressure applied by the end effector would vary with the thickness and makeup of the tissue being grasped.
Non electrosurgical endocutters such as those described in U.S. Pat. No. 5,597,107, employ a relatively stiff lower jaw member which includes a staple cartridge in conjunction with a more flexible upper member which acts as an anvil against which the staples are formed. In such instruments, the anvil is generally manufactured to be as stiff as possible, within the limits of size, materials and other design considerations and the spring rate of such an anvil may be, for example, in the range of 350-450 pounds per inch. A stiff anvil helps to ensure that the staples form properly when the instrument is fired. Spring rate, in terms of tissue compression forces in conventional staplers with gap spacing pins, is used in conjunction with the gap pin to create and maintain a minimum gap between the staple cartridge and the anvil, setting the height of the formed staple. Therefore, the designers of conventional stapling instruments with gap spacing pins are primarily interested in the formation of a simple beam with consistent gap to form consistent staples. In other designs, the gap pin is not used and the anvil is designed with sufficient stiffness to facilitate the formation of tissue. It would, therefore, be advantageous to design an electrosurgical instrument where the spring rate of the anvil is sufficiently stiff for the formation of staples while exerting a pressure in a range which facilitates the proper cauterization of tissue.
It is therefore an object of the present invention to provide a hemostatic electrosurgical instrument which can exert pressure in a range to efficiently provide improved hemostasis in multiple tissue types and thickness, e.g., in fleshy or vascular tissue areas, and high, low or combination impedance tissues. Hemostasis is used herein to mean generally the arresting of bleeding including by coagulation, cauterization and/or tissue joining or welding.
Another object of the invention is to provide an improved cutting and stapling device with an electrocautery means for tissue welding or cauterization along a cutting path wherein the device is adapted to grasp tissue and exert a pressure within a predetermined range in order to provide improved hemostasis prior to cutting the tissue.
These and other objects of the invention are described in an electrosurgical device having an end effector with opposing interfacing surfaces associated with jaws for engaging tissue therebetween, and two electrically opposite poles located on one or both of the opposing surfaces. The poles are isolated from each other with an insulating material, or, where the poles are on opposite interfacing surfaces, they may be offset from each other so that they do not directly oppose each other on interfacing surfaces. In particular, an electrosurgical device according to the present invention includes a substantially fixed lower jaw. Further, an electrosurgical device according to the present invention includes a substantially flexible upper jaw having a spring rate in the range of between approximately 200 pounds per inch and approximately 600 pounds per inch. More particularly, the spring rate of the upper jaw is approximately 275 pounds per inch.
An electrosurgical instrument of a preferred embodiment compresses tissue to a pressure within a predetermined range in a compression zone between a first interfacing surface and a second interfacing surface and applies electrical energy through the compression zone. The first interfacing surface is comprised of: a first pole of a bipolar energy source, which interfaces with the compressed tissue in the compression zone; and a second pole electrically isolated from the first pole and located on the same or opposite interfacing surface. Electrically isolated poles are defined herein to mean electrodes isolated from each other by an insulating material in the end effector and/or offset from each other on opposing surfaces.
In a preferred embodiment, the compression zone is an area defined by a compression ridge on one of the interfacing surfaces which compresses the tissue against the other interfacing surface. Also, there may be a compression ridge on both interfacing surfaces. A coagulation zone is defined by the first pole, the second pole, and an insulator insulating the first pole from the second pole. The second pole, located on one of the interfacing surfaces, is generally adjacent to the insulator on the same interfacing surface or across from the insulator on an opposing surface. This arrangement electrically isolates the two poles and enables the current path between the first and second poles to cross through a desired area of tissue.
It is believed that the tissue compression normalizes tissue impedance by reducing structural differences in tissue which can cause impedance differences. Compression also stops significant blood flow and squeezes out blood which acts as a heat sink, particularly when flowing through blood vessels. Thus, compression optimizes delivery of energy to tissue in part by enabling the rate of energy delivery to exceed the rate of dissipation due to blood flow. The arrangement of the electrodes, which make up the poles, is important to ensure that the current passing between the two poles passes though the compression zone. Also, insulation or isolation of the opposite poles from each other on the instrument permits tissue compression without shorting of the instrument poles or electrical arcing common in bipolar instruments.
In one embodiment of the present invention, the pressure initially applied to tissue in the compression zone is between approximately 30 pounds per square inch (psi) and approximately 250 psi. In a further embodiment of the present invention, the pressure initially applied to tissue in the compression zone is between approximately 75 psi and 250 psi. In a further embodiment of the present invention, the pressure initially applied to tissue in the compression zone is between approximately 115 psi and 185 psi.
Thus, the tissue compression and the arrangement of the electrodes permit more efficient cauterization and offer the advantage of achieving hemostasis in a wide range of tissue impedance, thickness and vascularity.
In an alternative embodiment of the invention, the first pole is located on a first interfacing surface of a first jaw and the second pole is located on the same jaw as the first pole, but not on the interfacing surface.
The present invention also provides a device capable of coagulating a line or path of tissue along or lateral to a cut line or a cutting path. In one embodiment, the first pole comprises an elongated electrode. The elongated electrode along with the adjacent insulator form a ridge to compress the tissue to be cauterized. The second pole is adjacent the insulator on an opposite side of the insulator from the first pole.
In one preferred embodiment, a cutting means for cutting tissue is incorporated into the device and the device provides hemostatic lines adjacent to the path of the cutting means. Of course, cutting may occur at anytime either before, during or after cauterization or welding. In one variation of this preferred embodiment, stapling means is provided on one or both sides of the cutting path.
In one embodiment, an indicator means communicates to the user that the tissue has been cauterized to a desired or predetermined degree.
In another embodiment, the coagulation is completed prior to any mechanical cutting, i.e., actuation of the cutting means. If an indicator means is used, once tissue is cauterized, the cutting means may be actuated to cut between the parallel bars while the rows of staples are applied to the tissue.
In another embodiment, the hemostatic device is incorporated into a linear cutter similar to a linear cutting mechanical stapler. In this embodiment the hemostatic device comprises two parallel and joined elongated electrode bars which form one pole, and a slot for a cutting means to travel between the bars. Optionally, one or more rows of staples may be provided on each side of the slot and bars to provide additional hemostasis. In operation, tissue is clamped between two jaws. Electrical energy in the form of radio frequency current is applied to the compressed tissue to cauterize the blood vessels along the two parallel bars.
Another embodiment provides a means for detecting abnormal impedance or other electrical parameters which are out of a predetermined range. For example, the means for detecting may be used to indicate when the instrument has been applied to tissue exhibiting impedance out of range for anticipated good coagulation. It may also be used for detecting other instrument abnormalities. It is possible to detect the abnormal condition, for example, by using comparisons of normal ranges of initial tissue impedance in the interface electronics. This could be sensed in the first few milliseconds of the application of RF energy and would not present a significant therapeutic dose of energy. A warning mechanism may be used to warn the user when the impedance is out of range. Upon repositioning of the instrument, the same measurement criteria would apply and if the tissue impedance was again out of range, the user would again be warned. This process would continue until the normal impedance range was satisfied and good coagulation could be anticipated.
Similarly another embodiment provides a tissue welding and cauterizing cutting device similar to an intraluminal stapler. Preferably, the poles are formed in two concentric circle electrodes separated by an insulator. The electrodes which make up the poles may be located on either the stapler cartridge or the anvil.
In one embodiment of the present invention, the pressure exerted by the anvil is a function of the spring rate of the anvil. By providing a xe2x80x9cpre-bendxe2x80x9d angle on the anvil it is possible to obtain a pre-load (at a zero gap.) A preferred value of preload is in the range of between 12 and 18 pounds with a preferred value of approximately 15 pounds. In one embodiment of the present invention, the spring rate of jaw 32 is between approximately 225 pounds per inch and approximately 350 pounds per inch. More particularly , the spring rate of anvil 18 on jaw 32 is preferably in the range of approximately 275 pounds per inch.
These and other objects of the invention will be better understood from the following attached Detailed Description of the Drawings, when taken in conjunction with the Detailed Description of the invention.